US20090103741A1

US20090103741A1 - Method of correction of acoustic parameters of electro-acoustic transducers and device for its realization

Info

Publication number: US20090103741A1
Application number: US11/920,602
Authority: US
Inventors: Raimonds Skuruls
Original assignee: Real Sound Lab SIA
Current assignee: Real Sound Lab SIA
Priority date: 2005-05-18
Filing date: 2005-12-14
Publication date: 2009-04-23
Also published as: AU2005331972B2; CN101194535A; EP1911324A1; US8121302B2; CA2608395A1; JP2008541654A; RU2419963C2; EP1911324B1; MX2007014017A; CN101194535B; JP5356022B2; EP1911324B8; WO2006123923A1; RU2007142625A; AU2005331972A1; LV13342B; HK1114294A1; CA2608395C

Abstract

The invention relates to the field of acoustics, in particular to methods and devices of correction of acoustic parameters of electro-acoustic transducers and can be applied for improvement of playback parameters of acoustic signals of various electro-acoustic transducers. The offered method of correction of acoustic parameters of electro-acoustic transducer is characteristic with determining of correction parameters of an electro-acoustic transducer by using acoustic power frequency response of electro-acoustic transducer, its evaluation is obtained by taking measurements on ambient surface of electro-acoustic transducer or its segment, measuring results are obtained from many discreet points of this surface or its segment, hereto spectrum of played acoustic test signal is being matched to the spectrum of interference at the measurement site. The device for correction of acoustic parameters of electro-acoustic transducer for the realization of the correction method is characteristic with the section for processing of measurements (4) of the measuring system (1) includes blocks for calculation of acoustic power frequency response of electro-acoustic transducer and for inverting of acoustic power frequency response for obtaining of impulse response of the corrector (2).

Description

This invention relates to the field of acoustics, in particular to methods and devices of correction of acoustic parameters of electro-acoustic transducers and can be applied for improvement of playback parameters of acoustic signals of various electro-acoustic transducers.
There are known devices and methods for correction of acoustic parameters of electro-acoustic transducer by using measurements of acoustic parameters of electro-acoustic transducers where correction is performed both automatically and with participation of sound operator. Disadvantage of the known technical solutions is relatively low precision of measuring and poor quality of correction results.
It is known that human ear perceives information about sound timbre from direct sound, namely, the sound coming directly from acoustic transducer and early reverberation of the sound that reaches listener in first 30 ms after direct sound but ignores other sound reverberation. Up to now used measuring devices do not differentiate and separate direct sound waves and early reverberation of sound waves from posterior reverberation of sound waves.
Wherewith, the known technical solutions for correction of acoustic parameters of electro-acoustic transducer that are based on evaluation results of sound pressure caused by electro-acoustic transducer do not reflect real problems of playback of electro-acoustic transducer. Also, changing the evaluation place of sound pressure caused by electro-acoustic transducer, sound pressure frequency responses highly vary in every place making the operator face insoluble problem—which of acquired sound pressure frequency responses to be used and which of parameters additionally to be corrected manually or to be processed differently. Because there is no specified algorithm for obtaining correction, this process starts to resemble art. Using these measuring results for correction of acoustic parameters of electro-acoustic transducer, new sound distortions are created because there is attempt to correct the interference expression of sound waves in certain place of the room in known technical solutions. Thus, that kind of correction of acoustic parameters of electro-acoustic transducer is incorrect and inadequate to the transmission distortions and irregularities of electro-acoustic transducer.
There is known method of measuring the parameters of loudspeaker (U.S. Pat. No. 4,209,672, 24.06.1980., “Method and apparatus for measuring characteristics of a loudspeaker”, IPC² H04R 29/00), according to which the measuring result of a perceived sound parameters is transformed from analogue form to a digital form, the acquired result is being exposed to the Fourier Transform, afterwards modified into absolute value, logarithmed and further filtered in order to eliminate the effect of interference and thus to increase the accuracy of loudspeaker parameters' measurements. Finally, the acquired result is being transformed into analogue form and written in memory accordingly, hereto the acquired result is being written repeatedly by back playing the test signal from the generator in certain time interval. Disadvantage of the given method lies in the fact that for adjustment there are being used measurements that do not reflect the sound distortions of the electro-acoustic system and filtration process does not differentiate sound distortions created by the electro-acoustic system from the ones created by the room. Thus, the calculated adjustment is inaccurate and the result of adjustment creates worse sound than before its making.
There is known an acoustic signal correction device (U.S. Pat. No. 5,581,621, 03.12.0996., “Automatic adjustment system and automatic adjustment method for audio devices”, IPC⁶H03G 5/00) that contains memory device for equalizer data keeping, audio device with programmable equalizer that selectively modifies audio signal accordingly to the equalizer data, the audio signal analyzer that generates bench signal which keeps in its memory pattern profile of the preferable frequency response that the audible sound output signal is being compared to. Hereto, the signal analyzer is connected to programmable equalizer and audio device but audio device generates audible sound signal accordingly to bench signal. Besides, the acoustic signal correction device contains tools for automatic equalizer data correction accordingly to collation results. Memory device keeps in memory frequency response pattern profile and adjustment results. Equalizer also contains tools that divide output signal into many frequencies' sub ranges. Disadvantage of the given range lies in the fact that for the correction of acoustic signals there are being used measurements that do not reflect the sound distortions of electro-acoustic system, wherewith adjustments create worse sound than before their making.
The closest technical solution that is assumed as prototype is an acoustic characteristic correction device (EP 0624947, 27.08.2003., “Acoustic characteristic correction device”, IPC⁷H03G 5/16) where known device consists of:

- Measuring block that includes Measuring Section consisting of: Signal Source with test signals written in memory, amplifier, playback device, measuring device, amplifier of tested signal, registrar that fixes received signals from the mentioned measuring device as well as includes processing part for determination of correction parameters;
- And Correction block that includes Control Section with correction parameters written in memory and Realization Block for entering the required parameters. Optimal parameters for concrete needs are supplied by making correction in zones, dividing frequency range in zones, hereto, one end of the zone covers beginning of others. Disadvantage of the known device lies in its limited functional options, insufficient measurements precision of electro-acoustic transducer and relatively bad sound of corrected playback signal. The relatively bad sound of corrected playback signal is connected to the fact, that the correction characteristics are defined inaccurately, because, firstly, for correction of acoustical signals there are used measurements that do not display real problems of sound quality perceived by the listener. Secondly, adequate correction parameters are evaluated subjectively by participation of operator that causes doubts about the objectivity of correction, and, thirdly, the known technical solution intends dividing frequency range into relatively broad zones that decrease number of samples on the frequency's axis, thus loosing information about characteristics changes of frequency response on the frequency axis.

The goal of invention is to increase playback quality of acoustic signal of various electro-acoustic transducers, to increase precision and speed of corrections of acoustic parameter of electro-acoustic transducer related to it, as well as to increase the validity of automatic correction with minimal participation of the operator.
The set target is being achieved with correction method of acoustic parameters of electro-acoustic transducer that contains measuring of the acoustic parameters of electro-acoustic transducer on the ambient surface of the electro-acoustic transducer or its segment, acquiring the measurement results from many discreet points of this surface or segment, processing of the acquired measurement results, calculation of acoustic power frequency response of electro-acoustic transducer according to the processing measurement results of the acoustic parameters of electro-acoustic transducer, determining the correction parameters of electro-acoustic transducer with the help of acoustic power frequency response of electro-acoustic transducer and acoustic signal correction.
The set target can also be achieved by:

- Evaluation of acoustic power frequency response of electro-acoustic transducer is being acquired by moving the measuring device consecutively from one discreet point of the electro-acoustic transducer's ambient surface to another, making measurements with the interval of 0.2÷3.2 seconds and by using test signal whose duration is within boundaries of 0.05÷3.2 s;
- In the site of evaluations of acoustic power frequency response of electro-acoustic transducer where one lower horizontal reflective surface is dominating, electro-acoustic transducer's acoustic parameters are being measured on the segment of electro-acoustic transducer's ambient surface, one side of which collides with the lower horizontal reflective surface, hereto the measurements' surface is perpendicular the direction to the electro-acoustic transducer whose parameters it is measuring;
- In order to acquire evaluation of acoustic power frequency response of electro-acoustic transducer in the site where there are several dominating surfaces, measurements are being made along the lines that connect candidly chosen point on the lower horizontal acoustic environment's reflective surface with candidly chosen point on every other acoustic environment's reflective surface;
- In order to acquire the evaluation of acoustic power frequency response of electro-acoustic transducer in the site where surfaces have complicated configuration, measurements are being made along imaginary circle line, which is placed in a vertical plane, athwart the direction to the electro-acoustic transducer and along horizontal diameter and vertical diameter of this imaginary circle line;
- In order to acquire the evaluation of acoustic power frequency response of electro-acoustic transducer in small rooms with parallel walls, measurements in the room are made cornerwise from its symmetry centre to the corners of that are farthest from the electro-acoustic transducer.
- Impulse reaction of each particular discreet measurement is processed by Window Function, hereto the width of Window Function is chosen in amplitude of 0.04÷0.12 s;
- Evaluation of acoustic power frequency response of electro-acoustic transducer is equalized in scale of logarithm frequency; hereto evaluation of acoustic power frequency response is equalized by equalization function of cosine impulse.

Set goal is achieved also by offering device for realization of correction of acoustic parameter of electro-acoustic transducer (see claim 11) consisting of

- Measuring System that contains Measuring Section consisting of signal sources with test signals written in memory for generation of mentioned test signals, amplifier of playback signals, measuring devices, amplifier of tested signals, registrar that records received signals from the mentioned measuring device, output of Measuring Section, as well as measurements processing section for determination of correction parameters and Interface Block;
- And corrector that involves Control Section with correction parameters written in memory and Realization Block of correction, hereto the measurements processing section involves: Impulse Reaction Calculation Block for performing of composition operation between output signal of Measuring System and Spectrum Inversion Function Block for calculation of impulse reaction, Window Function block that multiplies samples of impulse reaction signals with samples of Window Function in order to exclude effect of interfering components, Fast Fourier Transform block that computes Fast Fourier Transform from impulse reaction signal, defining frequency sample data array on each separate impulse reaction, synchronization block that synchronizes the beginning of input data of Fast Fourier Transform with highest values of impulse reaction, registrar that stores data array of frequency samples, Acoustic Power Frequency Response Calculation block that calculates acoustic power frequency response from the mentioned data array of frequency samples, re-sampling block that converts acoustic power frequency response from linear scale to logarithmic scale, display for exposing the calculated acoustic power frequency response, block that defines correction levels of ranges ends of acoustic power frequency response, equalizing block for acoustic power frequency response that serves for eliminating the effects of small irregularities and interferences of acoustic power frequency response, re-sampling block for transformation of power frequency response from logarithmic scale to linear scale, inverter for calculation of inverse value of power frequency response samples, Filtration Block for power frequency response samples that serves for obtaining total impulse reaction of corrector, inverse Fast Fourier Transform calculation block that calculates samples of impulse reaction of correction and sends data to normalized samples calculation block of impulse reaction, hereto the mentioned Realization Block calculates the composition operation between input signal of sound signal and impulse reactions of correction from Control Section, and sends the obtained calculation result to Sound Signal Output.

The device, in addition, can contain block for calculation of average value of synchronized impulse reactions, a block for calculation of time delay of groups, equalization block of group delay, block for calculation of phase corrector of frequency response from time delay frequency response and a block that adjusts the phase of acoustic power frequency response by multiplying the respective sample of acoustic power frequency response with the respective sample of acoustic power frequency response in complex form. The device can also contain several correctors.

Method of correction of acoustic parameters of electro-acoustic transducer and device for realization of the method is described in attached drawings, where:

In FIG. 1A there is described alternative scheme of discreet point disposition of measuring of acoustic parameters of electro-acoustic transducer in the site with one dominating—the lower horizontal reflective surface;

In FIG. 1B—alternative scheme of discreet point disposition of measuring of acoustic parameters of electro-acoustic transducer in the site where there are several dominating reflective surfaces;

In FIG. 2A—alternative scheme of discreet point disposition of measuring of acoustic parameters of electro-acoustic transducer in relatively small rooms with parallel walls;

In FIG. 2B—alternative scheme of discreet point disposition of measuring of acoustic parameters of electro-acoustic transducer in the site where reflective surfaces have complicated configurations;

FIG. 3—test signal form;

FIG. 4—total block diagram of correction device of acoustic parameters of electro-acoustic transducer;

FIG. 5—detailed block diagram of Measuring Section of Measuring System of acoustic parameters of electro-acoustic transducer correction device;

FIG. 6—detailed block diagram of Measurement Processing Section of Measuring System of acoustic parameters of electro-acoustic transducer correction device;

FIG. 7—acoustic power frequency response with indicated amplifications/decay of the ends;

FIG. 8—equalized acoustic power frequency response.

THE EXAMPLE OF REALIZATION OF THE INVENTION

The correction of acoustic parameters of electro-acoustic transducer is being made with the device described in FIG. 4 that consists of Measuring System 1 and at least one corrector 2, where Measuring System consists of Measuring Section 3 and, the measurements processing section 4 and Interface Block 5, but corrector 2—from Control Section 6, Realization Block 7 with Sound Signal Input 8 and Sound Signal Output 9. The correction of acoustic parameters of electro-acoustic transducer by offered method is being made as follows:
Schematically described Signal Source 10 (FIG. 5) with in memory written acoustic test signals repeatedly plays back test signal whose spectrum is balanced with interference spectrum in the site of measurements. Therefore, test signal is being chosen with higher energy spectrum in the lower frequency area, where the interference energy is higher, as well as such that has enough small highest value relation with average value. In this example of realization of the invention such signal is chosen with whom the signal/noise relation in range of 20÷30 dB can be obtained. The chosen duration of played test signal (FIG. 3) is 0.05 s.
Further, the played acoustic test signal is amplified with amplifier 11 and is played with electro-acoustic transducer 12 that is correctable electro-acoustic transducer. Measuring device 13 perceives the played acoustic test signal in discreet points of acoustic environment embraced by electro-acoustic transducers with 0.4 s time interval. Hereto, the measurements are taken on segment of ambient surface of electro-acoustic transducer by evenly moving measuring device from one measuring point to another, like it is shown schematically in FIG. 1A. Taking measurements of parameters of electro-acoustic transducer in the rooms where there are several asymmetrically placed dominating reflective surfaces, the measuring device is being moved along lines that connect point on the floor with the point on dominating reflective surface of each room, as it is shown in FIG. 1B. Taking measurements of parameters of electro-acoustic transducer in the rooms with parallel walls, the measuring device is being moved cornerwise (see FIG. 2A) from symmetry centre to corners of the room that are farthest from electro-acoustic transducer. Taking measurements of parameters of electro-acoustic transducer in the rooms where reflective surfaces have complex configuration or where taking of measurements is complicated by objects existent in the room, the measuring device is being moved like it is shown in FIG. 2B-along imaginary circle line, which is placed in a vertical plane, athwart the direction to the electro-acoustic transducer and along horizontal diameter and vertical diameter of this imaginary circle line.
Further, acoustic test signal perceived by Measuring Device 13 through Amplifier 14 comes in Registrar 15 where all signals obtained in measuring points are entered and through Output 16 are entered in Input 17 of Measurement Processing Section 4 for calculation of parameters of Correction Filter (FIG. 6). Further, signal is entered in the Impulse Reaction Calculation Block 18 for performing composition operation between signal of output 4 of Measuring Section and Spectrum Inversion Function stored in the Spectrum Inversion block 19, for calculation of impulse reaction in order to calculate impulse reactions of electro-acoustic transducer in the measuring points. Further, signal is entered in Window Function block 20 in order to exclude such distortion factors as effects of non-linear and reverberation. Window Function block 20 multiplies samples of impulse reaction signals with samples of Window Function stored in memory of block 21.
Window Function is being utilized so that at the impulse reaction highest values' Window Function is 1 but at the lowest impulse reaction values the Window Function is leaning towards 0 thus excluding interference factors from the measurements, such as non-linearity and reverberation. With Window Function that is longer in time, higher distinction of measurements in the area of low frequency is possible while as a result, the effect of reverberation increases. But with Window Function that is shorter in time, the impact of room decreases although information about the lower frequency area starts to disappear.
After the processing of signal in Window Function block 20 the acquired results are being entered in Fast Fourier Transform block 22 that calculates Fast Fourier Transform from the impulse reaction signal determining frequency sample array for each separate impulse reaction, in synchronization block 23 that coordinates the beginning of Fast Fourier Transform input array with highest value of impulse reaction. The acquired data is then being entered in the Registrar 24 that stores frequency sample array, the acoustic power frequency response is being calculated in block 25 that calculates acoustic power frequency response from the mentioned frequency sample array and in Re-sampling Block 26 that transforms acoustic power frequency response from linear frequency scale into logarithmical frequency scale. The calculated acoustic power frequency response is being displayed in Display 27. Afterwards, the calculation results are being entered in block 28 that determines the correction levels (see FIG. 8) of acoustic power frequency response's range ends. Correction levels of range ends in the lower frequency area (L_LF) and in the high frequency area (L_HF) are being chosen depending on correctable electro-acoustic transducer's ability to play back lower and high frequency signals without overload. In this example of realization of the invention, the correction levels of range ends are being chosen in the area −5 dB of lower frequency and area −6 dB of high frequency area.
Further the calculation results are being entered in Acoustic Power Frequency Response Leveling Block 29 that serves for elimination of the effect of small irregularities and interference of the acoustic power frequency response (see FIG. 8) and in Re-sampling Block 30 for transforming of power frequency response from logarithmical scale into linear scale. Besides, before the Fast Fourier Transform Block 22 the acquired results additionally are being entered in block 31 that calculates the average value of synchronized impulse reaction, sends it to block 32 for calculation of Group Delay Time, to the Group Delay Leveling Block 33, block 34 that calculates Phase Frequency Response of corrector 2 from group delay time frequency response, and block 35 that corrects acoustic power frequency response phase by multiplying the respective acoustic power frequency response sample with the respective phase frequency response sample in complex form and then sends to Inverter 36 for calculation of inversed value of acoustic power frequency response sample. Afterwards, the acquired results are being sent to power Frequency Response Sample Filtration Block 37 that serves for acquiring of total impulse reaction of corrector 2, afterwards are being sent to Inverse Fast Fourier Transform calculation block 38 that calculates impulse reaction samples of corrector 2 and sends data to Impulse Reaction Normalized Sample Calculation Block 39 and to Measurements Processing Section 4, exit 4. The acquired data array further is being sent to Interface Block 5 that saves the impulse reaction sample array received from the processing section and afterwards is being sent to corrector 2 Control Section 6 for saving of different correction impulse reactions. From Control Section 6 acquired results go into Realization Block 7 that calculates composition operation between the signal of Sound Signal Input 8 and the correction impulse reaction received from the Control Section 6. Further the correction result is being channeled to Sound Signal Output 9, wherefrom it is being sent to the amplifier and the respective electro-acoustic transducer for playback.
Constant transmission coefficient between input signal of corrector and reflected acoustic power of electro-acoustic transducer on different working frequencies is reached by making corrections of electro-acoustic transducer with the offered method and device. Besides, undistorted power of sound Signal Source transmission to acoustic power is provided and deep correction of timbre distortions of electro-acoustic transducer does not make new sound defects, and as a result, working in different conditions and different places, timbraly distortion-free, natural sound is gained.

Claims

1-12. (canceled)

13. A method of improving the performance of an electro-acoustic transducer, comprising the steps of:

generating an acoustic test signal through the electro-acoustic transducer;

measuring the acoustic test signal at multiple points on an ambient surface around the electro-acoustic transducer to create measured acoustic data;

calculating an acoustic power frequency response of the electro-acoustic transducer based on the measured acoustic data; and

determining a correction impulse response for the electro-acoustic transducer based on the acoustic power frequency response.

14. The method of claim 13, further comprising the step of applying the correction impulse response to a sound signal input to generate a sound signal output for playback through the electro-acoustic transducer.

15. The method of claim 14, wherein the step of applying the correction impulse response comprises the step of performing a convolution operation between the correction impulse response and the sound signal input.

16. The method of claim 13, wherein the generating step comprises the step of generating the acoustic test signal of duration of 0.05 to 3.2 seconds.

17. The method of claim 13, wherein the measuring step is performed at the interval of 0.2 to 3.2 seconds for each of the multiple points.

18. The method of claim 13, wherein the measuring step comprises the step of moving a measuring device through the multiple points on the ambient surface around the electro-acoustic transducer.

19. The method of claim 13, wherein the calculating step comprises the steps of:

calculating an impulse response of the electro-acoustic transducer based on the measured acoustic data;

determining a frequency sample array based on the impulse response; and

calculating the acoustic power frequency response of the electro-acoustic transducer based on the frequency sample array.

20. The method of claim 19, further comprising the step of processing the impulse response by a Window function prior to performing the step of determining a frequency sample array.

21. The method of claim 20, wherein the width of the Window function is between 0.04 seconds and 0.12 seconds.

22. The method of claim 19, wherein the step of calculating an impulse response comprises the step of performing a convolution operation between the measured acoustic data and an inverse spectrum function.

23. The method of claim 19, further comprising the step of eliminating small irregularities and interference effects in the acoustic power frequency response.

24. The method of claim 19, further comprising the step of determining a correction level at the range ends of the acoustic power frequency response.

25. The method of claim 13, wherein the determining step comprises the steps of:

correcting the phase of the acoustic power frequency response;

calculating an inverse value of the corrected acoustic power frequency response;

acquiring a total impulse response by processing the inverse value of the corrected acoustic power frequency response; and

processing the total impulse response to generate the correction impulse response.

26. The method of claim 26, wherein the step of correcting the phase of the acoustic power frequency response comprises the steps of:

calculating an average value of synchronized impulse response based on the impulse response;

determining a group delay time based on the average value of the synchronized impulse response;

processing the group delay time to determine a phase frequency response; and

multiplying the acoustic power frequency response with the phase frequency response in complex form.

27. The method of claim 13, further comprising the step of displaying the acoustic power frequency response of the electro-acoustic transducer.

28. The method of claim 13, further comprising the step of smoothing the acoustic power frequency response in scale of logarithmic frequency.

29. The method of claim 28, wherein the smoothing step comprises the step of applying a smoothing function of cosine impulse.

30. The method of claim 13, wherein, in the presence of a dominating lower horizontal reflective surface in an acoustic environment, the ambient surface lies perpendicular to the direction to the electro-acoustic transducer and one side of the ambient surface collides with the lower horizontal reflective surface.

31. The method of claim 13, wherein, in the presence of several dominating surfaces in an acoustic environment, the multiple points on the ambient surface are selected from lines connecting randomly chosen point on the lower horizontal reflective surface with randomly chosen point on every other dominating reflective surface.

32. The method of claim 13, wherein, in the presence of complicated surfaces in an acoustic environment, the multiple points on the ambient surface are selected from an imaginary circle placed in a vertical plane, athwart the direction to the electro-acoustic transducer, and along the horizontal diameter and vertical diameter of the imaginary circle.

33. The method of claim 13, wherein, in the presence of parallel walls in a room, the multiple points on the ambient surface are selected from lines connecting the symmetry centre of the room to the corners of the room.

34. A device for improving the performance of an electro-acoustic transducer, comprising:

a measuring section for measuring acoustic test signals from the electro-acoustic transducer to create measured acoustic data;

a measurement processing section for calculating an acoustic power frequency response of the electro-acoustic transducer based on the measured acoustic data from the measuring section, and processing the acoustic power frequency response to generate a correction impulse response; and

a correction filter for applying the correction impulse response to a sound signal input to generate a sound signal output for playback through the electro-acoustic transducer.

35. The device of claim 34, wherein the measuring section comprises:

a measuring device for receiving the acoustic test signals;

an amplifier; and

a memory for storing the measured acoustic data.

36. The device of claim 34, wherein the measurement processing section comprises:

an impulse response calculator for calculating an impulse response of the electro-acoustic transducer based on the measured acoustic data from the measuring section;

a Fast Fourier Transform calculator for determining a frequency sample array based on the impulse response;

an acoustic power frequency response calculator for calculating the acoustic power frequency response of the electro-acoustic transducer based on the frequency sample array;

a frequency response phase adjustor for correcting the phase of the acoustic power frequency response;

an inverter for calculating an inverse value of the corrected acoustic power frequency response;

an acoustic power frequency response sample filtration block for acquiring a total impulse response based on the inverse value of the corrected acoustic power frequency response; and

a block for processing the total impulse response to generate the correction impulse response.

37. The device of claim 34, wherein the correction filter comprises:

a control section for receiving and storing the correction impulse response; and

a realization block for performing a convolution operation between the correction impulse response and the sound signal input to generate the sound signal output.

38. The device of claim 36, wherein the measurement processing section further comprises a Window function processor for applying a Window function to the impulse response from the impulse response calculator to exclude interference effects, and forwarding the processed impulse response to the Fast Fourier Transform calculator.

39. The device of claim 36, wherein the impulse response calculator is configured to perform a convolution operation between the measured acoustic data from the measuring section and an inverse spectrum function to generate the impulse response.

40. The device of claim 36, wherein the measurement processing section further comprises an acoustic power frequency response smoothing block for eliminating small irregularities and interference effects in the acoustic power frequency response.

41. The device of claim 36, wherein the frequency response phase adjustor comprises:

a block for calculating an average value of synchronized impulse response based on the impulse response;

a block for determining a group delay time based on the average value of the synchronized impulse response;

a block for processing the group delay time to generate a phase frequency response; and

a block for multiplying the acoustic power frequency response with the phase frequency response in complex form.

42. The device of claim 34, further comprising a display for displaying the acoustic power frequency response of the electro-acoustic transducer.